1. Field of the Invention
The present invention relates generally to a method of conveying, controlling and dispensing thermoplastic material. More particularly, this invention pertains to a process and an apparatus for conveying, filtering, and feeding a high throughput of solid thermoplastic adhesive material with continuous, smooth, controlled and batch flow of the hot melt resin adhesive resulting in minimal degradation of the molten thermoplastic material into a dispensing device capable of preventing dripping of the molten hot melt glue upon controlled shutoff of the dispensing process. The method and apparatus of this invention reduces both the maintenance and downtime of the process in comparison to currently available systems.
2. Description of the Prior Art
Many thermoplastic adhesive materials degrade or oxidize when exposed to heat or oxygen for extended periods of time. It is desirable to minimize duration of time that hot melt glue remains in a molten state to avoid degradation of its adhesive properties. This is achieved by some application systems by balancing the rate of application of the hot melt glue with the thermoplastic adhesive material melt rate and conveying of the system U.S. Pat. No. 3,981,416 discloses an apparatus similar to the device in U.S. Pat. No. 3,964,645 patented by the same inventor. These two patents claim a novel heating grid meter and an infeed system, which forcibly moves the molten hot, melt glue into the pump inlet.
The primary objective of this invention is to provide batch conveyed, smooth, controlled and uninterrupted flow of the hot melt adhesive resulting in no degradation or oxidation of the molten adhesive material while fully meeting the requirements of a high throughput application system.
Another objective of this invention is to provide an initial filtering method to screen out any contaminants or foreign particles from the thermoplastic adhesive chips, chiclets, or pellets being fed into the hot melt material system. Prior systems using filters or screens have maintenance problems and downtime associated with cleaning the screens in order to avoid clogging and to attempt to provide uninterrupted flow of the solid glue material from a bulk source.
Another traditional problem with thermoplastic adhesive systems is the clogging of the glue chip hopper and a build-up of partially solidified glue in the feed lines from the hopper leading directly to the glue melter apparatus. This phenomenon occurs because heat flows up the lines from the glue melter device to the glue chip hopper. Various heat-insulating techniques have been used to greatly reduce this problem. A build-up of partially solidified glue in these lines results in downtime to remove the material and excess maintenance costs. U.S. Pat. No. 5,447,254 discloses an intermittent dispensing apparatus, which is equipped with a dispensing head in the discharge passageway whereby the exhaust air from the dispenser is directed into the air passageway so as to blow off and remove the excess liquid hot melt glue material from the nozzle dispensing head. An air passageway extends through the valve upstream of the discharge end of the dispenser such that pressurized air is directed into the air passageway during the shut-off cycle whereby the dripping and drooling hot liquid material is effectively blown out. This apparatus is a novel dispenser, which prevents dripping of the molten hot melt glue upon shut off of the application dispenser. However, this patent does not address the problem of a build-up of partially solidified glue in the lines leading into the glue melter itself.
Another objective of this invention is to provide an integrated conveying system for thermoplastic adhesive materials from a bulk source such as a Gaylord container or a 55 gal. drum container of the raw materials into the hot melt glue chip conveying system which permits fully emptying the thermoplastic adhesive materials from the source. Devices for sensing the level of solid materials in various containers have long been used. The resulting levels of such solid materials have been detected and displayed. No previous hot melt glue chip conveying system has used the solid material level sensed in a bulk material source to automatically activate other component systems such as vibration, vacuum, or conveyors to fully empty the bulk material source.
Other hot melt glue chip conveying systems consist of devices such as in U.S. Pat. No. 5,685,911 which reveals an apparatus for intermittently applying discrete patterns of hot melt glue onto substrate areas that require such defined discrete glue patterns such as book spines, pinch bottom bags, sift-proof cartons and the like. In U.S. Pat. No. 5,814,790, the invention is for an apparatus and method for supplying hot melt glue using a plurality of hoppers with controlled heating zones with temperature sensor devices for non-uniform application of heat to the thermoplastic material during the several stages of melting and dispensing process. This device is for an apparatus, which receives a partially melted thermoplastic material and has four additional heaters connected to a progressive staged heating grid. This patent does not address the entire hot melt glue chip conveying system nor does it disclose the overall system required for delivery of the solid glue material to the very first stage apparatus therein.